Climate Science Glossary

Term Lookup

Settings

Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup

Term:

Settings

Beginner Intermediate Advanced No DefinitionsDefinition Life:

All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 3 October 2011 by Steve Brown

NOTE: This is the fourth article of a five-part series on what we can learn from the Last Interglacial time period. Understanding this period may provide clues on how the environment may respond to similar conditions in the future. In the first post, we described the conditions that exisited during the Last Interglacial. In the second post, we looked at the key factors for making it a warm period. In the third post, we looked at how sea-levels rose as a result of melting ice-sheets. In this post, we examine how the Last Interglacial oceans influenced the climate.

In the previous posts we learned that the Last Interglacial, also known as the Eemian in Europe, was significantly warmer than today in large regions of the Northern Hemisphere, and may have been around 1oC warmer globally. The main reason for this warmer climate was an increased amount of energy from the Sun being received at high northern latitudes due to Earth's orbital configuration, plus Earth had an increased capacity to absorb heat due to vegetation changes and reduced ice and snow cover. This warmer climate led to significant melting of the Greenland and Antarctic Ice Sheets. As well as contributing to a global sea-level rise of several metres, the large volume of meltwater released to the ocean also had an effect on the climate.

It's long been known that the Gulf Stream has a significant role in maintaining a mild climate in Northern Europe by the transport of heat far into the North Atlantic. The Gulf Stream is part of a larger circulation system called the Atlantic Meridional Overturning Circulation (AMOC). The AMOC is closely related to the thermohaline circulation, which is driven by temperature and salinity changes. Meridional Overturning Circulation includes the action of wind, as well as density changes through differences in temperature and salinity in order to drive the ocean currents.

In recent years there has been a huge debate on how global warming may impact the Gulf Stream and the AMOC. A major consideration is the potential for a slowdown or stop of the AMOC in response to freshwater from the melting of the Greenland Ice Sheet, which lowers the density of the surface waters and puts the brakes on the thermohaline component of the AMOC. The AMOC has a considerable influence over European climate from the northward heat transport by the Gulf Stream and a slowdown or halt of the AMOC could have a large impact on climate and even induce abrupt climate changes (Alley et al, 2002; Alley, 2007). The IPCC Assessment Report 4 considered various models, estimating up to a 50% slowdown in the AMOC by 2100, though none predicted a complete halt. More recent studies support the view that it is very unlikely that the AMOC will undergo any abrupt transition this century (Allison et al., 2009). Though, between 1957 and 2004 there are indications of a 30% slowdown in the AMOC at 25oN (Bryden et al., 2005). Keenlyside et al. (2008) forecasts that the AMOC will weaken over the next decade, but they argue that large uncertainties exist in previous measurements of AMOC variability due to poor observation and modelling analyses. Recently, Willis (2010) used satellite observations of sea surface height and sensor buoy observations of velocity, salinity and temperature of the Atlantic Ocean at 41oN and found no significant change in the AMOC strength between 2002 and 2009. Despite interannual fluctuations, observations show that it's unlikely there has been any significant slowing of the AMOC during the past 20 years.

Surface freshwater plays an important role for ocean circulation by its influence on the formation of deep water masses. A stronger deep circulation may increase northward heat transport by the AMOC, while a weaker deep circulation may promote less northward heat transport (Born et al., 2009). Barreiro et al. (2008) found that northern Atlantic waters have freshened rapidly in the past few decades and heat transported northward by the thermohaline circulation has decreased. It's expected that this freshening could increase further through intensified high-latitiude precipitation and glacial melt-water related to global warming. Vellinga et al. (2008) examined various model results that attempt to quantify how the AMOC responds to different melt-water fluxes from Greenland. In one model a large enough flux, or rate of flow, of melt-water to shutdown the AMOC was created, which resulted in a cooling of surface air temperature in excess of 15oC over the Norwegian and Barents Seas, with a lesser degree of cooling over the whole hemisphere. Most models that investigate increasing greenhouse gas scenarios predict that the AMOC will slow down as a result of such forcing (Driesschaert et al., 2007; Meehl et al., 2007). However, other model results suggest that anthropogenic aerosols may have delayed a greenhouse gas induced weakening of the AMOC by reflecting inbound solar radiation and partially offsetting greenhouse gas warming.

Hodell et al. (2009) present evidence for a slowdown of the AMOC during the early part of the Last Interglacial from proxy data taken from marine core sediment in the Iceland basin. They suggest that slow current speed detected at the locality may have been the result of an increased meltwater flux in the Nordic Seas due to peak summer insolation. Their findings indicate that the slowdown of circulation happened when climate was warmer than present and the Greenland Ice Sheet was in retreat. This slowdown is supported by computer modelling studies of the Last Interglacial, which estimates that the AMOC was ~20% weaker between 127 and 125 ka (Groger et al., 2007). Using pollen based climate reconstructions, Field et al. (1994) suggest that instability of the AMOC due to high summer insolation and increased precipitation may have led to cold winters in northern Europe. However, this situation ended when the freshwater flux from ice-sheet melting decreased and a newly enhanced thermohaline circulation in the Atlantic was likely to have extended the interglacial warmth during the latter part of the Last Interglacial. This additional heat transport may also have increased snowfall in Arctic regions through enhanced evaporation and precipitation, facilitating the return to glacial conditions (McManus et al., 2002).

According to Felis et al. (2004), the major influences on climatic variability in the Northern Hemisphere are the Arctic Oscillation and North Atlantic Oscillation, which are regions of atmospheric pressure differences that can guide weather systems on a seasonal basis. The North Atlantic Oscillation is a fluctuation of atmospheric pressure measured between Iceland and the Azores, which can determine the seasonal weather patterns of Europe, North Africa and the Middle East. A large pressure difference, called a high-index state, in the North Atlantic Oscillation typically causes the Gulf stream to flow stronger, bringing warmer and wetter weather to Europe. A low pressure difference (a low index state) does the opposite, with generally drier and cooler weather to Europe. The Arctic Oscillation can determine the track of the jet stream, which either flows West to East, keeping the cold polar air trapped in the Arctic, or it loops southward bringing cold polar air to Europe. A climate record of the Last Interglacial from corals in the Red Sea show evidence of a high index state of the North Atlantic Oscillation leading to increased seasonality between winter and summer temperatures in the Middle East compared to the present day. Warmer summer temperatures were a direct result of increased summer insolation, with the colder winters possibly related to North Atlantic Oscillation influences such as increased cold air advecting from the North.

Lisiecki et al. (2008) analysed orbital responses in proxy indicators of oceanic overturning and found that the AMOC is sensitive to maxima in the obliquity and precession components of the Earth's orbit around the Sun. The component of the AMOC in the Nordic Seas show signs of responding rapidly to orbital forcing.

North Atlantic Deep Water (NADW) is a distinct mass of deep salty and cold water that forms from the growth of Arctic sea-ice, which leaves behind a dense brine that sinks and contributes to the thermohaline circulation. A link between Earth's orbital eccentricity and NADW production with high eccentricity leading to low production of NADW and vice versa is proposed by Crowley and Kim (1992). This orbital influence may possibly be explained by circulation changes from strong temperature contrasts between land and sea. Low production of NADW will decrease thermohaline circulation. Some climate models of the Last Interglacial indicate that a high-index state of the North Atlantic Oscillation, bringing cool summers and mild winters to Europe, is favoured due to the configuration of orbital parameters. Less vigorous ocean circulation in the North Atlantic has been associated with positive phases of North Atlantic Oscillation. If peak summer insolation during the early Last Interglacial favoured a persistent positive North Atlantic Oscillation, then this may have contributed to slow circulation from ~128 to 124.5 ka. (Hodell et al., 2009).

Seidenkrantz & Knudsen (1997) proposed that higher sea level may have allowed warm water from the North Atlantic Drift, which forms from the northerly reaches of the Gulf Stream, to pass through the English Channel into the North Sea during the Last Interglacial. A stronger North Atlantic Drift would increase the flow of warm water into the North Sea past northern Britain. Sea-surface temperatures in the English Channel were 1 to 3oC warmer during the Last Interglacial compared to today, while in the Kattegat between Denmark and Sweden, sea-surface temperatures were up to 8oC higher than today. These higher sea-surface temperatures may be explained by a stronger North Atlantic drift, and more open connections between the North Sea and White Sea due to higher sea level and the formation of the Eemian Sea (Burman & Passe, 2008).

Figure 4: Meridional Overturning Circulation in the Atlantic during the late Eemian (illustration by jg. Source for Earth's topology: NASA/JPL-Caltech)

Pelejero et al (2003) present a proxy derived record of sea surface temperatures to the west of New Zealand that covers the Last Interglacial period. They find that sea surface temperature was up to 4.5oC warmer than present and that the latitudinal temperature gradient for the southwest Pacific is consistent with persistent La Nina and positive Southern Oscillation Index conditions. They highlight other evidence from corals in Indonesia and Papua New Guinea that indicate El Nino Southern Oscillation (ENSO) variability was biased towards more extreme La Nina events during the Last Interglacial compared to the preindustrial Holocene. According to Hughen et al. (1999), an isotopic analysis of fossil coral in Indonesia from 124 ka suggest a robust ENSO variability that matches ENSO behaviour in the recent past. The similarity appears to diverge from observations of ENSO variability since the 1970's indicating that ENSO since then is anomalous to natural variability and possibly a sign of changes due to recent warming.

This series of posts have looked at detailed and diverse aspects of the evidence that builds a picture of the Last Interglacial and some insight into the reasons why there were significant environmental impacts. Can the Last Interglacial give us an insight into what may be in store for us in a warming world? We'll discuss the relevance of the Last Interglacial to the future in the final post of this series.....

Comments

Like the previous articles, this one is very well done. I have been waiting a while for this article and am glad that it has finally arrived.

I still argue that you are going through a lot of extra work trying to explain the warmer NH climate during the Eemian by using vegetation and ocean currents when insolation is such a direct cause for the warmer climate. The weaker SH insolation at the same time also explains the cooler SH during the Eemian, but aside from that complaint, this is an interesting article.

I fully agree that the ocean currents were unstable during the Eemian. This is evident as well from the NGRIP ice core. It shows some very rapid step function changes in temperature ~119,000, 116,000 and 111,000 YBP. The NGRIP shows such changes through the last glacial as well as during the early Holocene. Changes to the ocean currents are clearly the most likely cause of those temperature changes. Much like what happened 8,200 years ago and on a much smaller scale during the Younger Dryas.

Based on the full length of the NGRIP data, the past 10,000 years have been unusually stable (which I propose is due to the slow rate in change in 65N insolation). There have been 20+ rapid changes in the NGRIP data which covers the last 125,000 years. If each of those were associated with a change in the ocean current, we are about due for another.

If such changes in the ocean current are natural and have happened with regular frequency over the past 125,000 years, then why should we expect that type of behavior to change now or in the future?

The Eemian insolation and temperature was comparable to today's climate when it experienced its first rapid drop ~119,000 years ago. Such a drop should be expected because that is exactly what the Earth has done in the past.

Overall this series is probably the most useful set of articles I have ever found on this website. ;-)

Is there a period in the proxy record of past climate, where if we drew a graph showing Global average Temp and CO2 over time and overlay it on a graph of today's Global average Temp and CO2 over time, we would not be able to tell the difference between the graphs apart from the time(historic period). If not at what period in the past were we closest to the present day with regard to CO2 and Temp.

00

Response:

[DB] Try this:

Note that at no point in the last 800,000 years has CO2 levels exceeded 298.7 ppm; thus current CO2 levels are far, far outside the bounds of natural variation:

DB thank you for your response. If I wished to inform myself as to the future by using the past I would look for a point at which conditions intersect. One could then extrapolate those conditions into the future. My understanding is that Anthropogenic or natural variations in CO2 are indistinguishable with regard to their effect on the climate. I am genuinely interested to see what past conditions were closest to present conditions. I am trying to do the research for myself but it is difficult without the relevant software to produce the graphs accurately and thought that someone else might have done so already thus saving me the work.
If in the past there were no meaningful conditions that match the present because of tectonic changes etc how can we use these conditions to extrapolate the future with any certainty.
If I am wrong in this assumption I would be glad to be corrected.

Thanks for your kind comments about the series. However, it seems that you are still bending over backwards to exclude any explanation other than the Sun as being the cause of warmer climates. I'll refer you back to my responses to your earlier comments in Part Two of the series, in particular the fact that modelling studies show that albedo effects from vegetation changes quadrupled the orbital insolation effect during the Eemian. Feedback effects can't be wished away. Also, it's not me who is working too hard to explain the NH warming This series is merely an unbiased review of the range of published literature on the topic. The explanation I'm giving is broadly that of the cumulative body of work on the subject.

@FundMe -

I'm afraid I can't think of a period off the top of my head where temperature and CO2 match closely to what is currently happening. Marine Isotope Stage 11 Interglacial around 400,000 years ago may be a better analogue for the next century compared to the Eemian / MIS 5e Interglacial, as the orbital configuration is a much better match to the neasr future. Also, MIS 11 was a much longer warm period and may have been slightly warmer than the Eemian. However, atmospheric CO2 was still at a pre-industrial level and no higher than it was during the Eemian.

The last period I can think of where there was a significant increase in atmospheric CO2 and a shift to a much warmer climate in a relatively short period of time would be the Paleocene-Eocene Thermal Optimum around 56 million years ago.

The problem with finding a past period that is a close analogue of the present day is that there are numerous factors that affect climate: Continental configuration, configuration of sea-ways between oceans, volcanism and tectonic activity, mountain uplift and rates of rock weathering, distribution of vegetation, type of vegetation and marine organisms, energy output of the Sun, Earth's orbital configuration, mix of greenhouse gasses etc. Unfortunately there are no periods in the past where every one of these factors has been similar to today. There is also the matter of no period in Earth's history that has seen a very rapid increase in the number of mammals with the ability to cause rapid changes in land use and short-circuit the long-term carbon cycle in the space of a few hundred years.

From Steve Brown @ 4:There is also the matter of no period in Earth's history that has seen a very rapid increase in the number of mammals with the ability to cause rapid changes in land use and short-circuit the long-term carbon cycle in the space of a few hundred years.

Am I right in assuming that we can explain the past by examining the proxy record while taking into account all of the various factors tectonics, orbit, etc etc but cant use any of the record to extrapolate the future because of the vast differnces found. As the saying goes "The Past is another Country" but I think in this case we might as well say "The Past is another Planet".

No, the past is not "another planet." Paleoclimate provides vital clues to what may happen as we tinker with the environment - given that we understand the impacts of such things as tectonics and orbital parameters.

But on the time scale of the next century, of what concern are tectonic and orbital changes?

I think you could arguably say the very distant past is "another planet", but the more recent past i.e. the past few million years is very definitely the "same planet". The Earth during the Last Interglacial is virtually identical to todays Earth - the continents and oceans are in virtually the same place, atmospheric composition is similar to the recent past, and it pretty much has the same species of plant and animal (barring those that have recently gone extinct). So looking at the proxy record of the recent past can be extremely valuable for allowing us to constrain climate sensitivity to various forcings, as well as understanding the rate of change and responses in the environment.

All the various factors that can have an effect on climate change operate on wildly different timescales. The increasing energy output from the Sun has happened over billions of years. The sequestration of carbon and changes to atmospheric compostion has taken hundreds of millions of years of plant evolution. Plate tectonics changes contintental configuration over tens to hundreds of millions of years. The increased rock weathering from mountain uplift, leading to sequestration of atmospheric CO2 to the ocean and formation of limestone also happens over millions of years. Changes in insolation due to orbital configuration happens over thousands to tens of thousands of years, ice-albedo feedbacks operate over decades to centuries, global land use changes and massive clearance of forests by humans happens over 8000 years, short-circuiting the long term carbon cycle leading to the greatest rate of increase in atmospheric CO2 in Earth's history happpens over a few decades.....

I think your sticking point is that you'd like an exact template to which to compare today's events. This doesn't exist, but we have a very good understanding of where the differences lie, enough to project (with research, intelligence and thought) what is expected to happen.

This is no different from getting your car fixed or going to the doctor. You cannot demand that the mechanic or doctor point you to a car/patient with the exact same symptoms; same make/model/year, number of miles, funny noises, repair history, etc., or for a patient the same age, sex, weight and family history, environmental issues, same symptoms, exact same reaction to drugs, etc.

In particular, you'll find that doctors and surgeons are even loathe to give you a percent chance of success for a treatment because of this. There are too many variables. They know what they're doing, and that their course of action is justified, but they are never going to be able to justify it to the layman by saying "meet Mr. Jones here, he is exactly like you, and the surgery worked perfectly for him."

Many, many things in life are too complex and have too small a sample size to predict by saying "ah ha, this is exactly the same, and this is what happened then, so..."

The ancient philosophers - mostly Greek - determined that if two things have every single detail in common then they must be one and the same thing. Let me put it this in a modern way: any two atoms whatsoever cannot be exactly identical in every property if they occupy different locations in space or time.
The scientific principle of the discovery of common features and formulation of sets of things having common properties is based in ordinary human cognition. It was used by the ancient Greeks to discover rules of logic, rhetoric and grammar and to discover universal laws of nature.
A basic assumption of science is that what was common to a group of things in the past and what is common now will be common in the future.
It doesn't matter if a black cloud is shaped like a human face or a banana: it will almost certainly rain on somebody's parade. Some features or properties not held in common are entirely irrelevant to predictability.

125,000 years ago is far to short a period of time for the Earth to be different in any physical way. The differences in the continents would be measured in tens of meters at the most which is not enough for the Earth to be considered a different planet.

The last time the physical characteristics changed enough to make a large difference was 34 million years ago when the Drake Passage was opening between South America and Antarctica.

Two extra changes that were relevent on small million year timescales. Creation of the Isthmus of Panama 3-5 million years ago, closing the seaway between the Pacific & Atlantic. Given how significant the North Atlantic Conveyor system is to regional and even global climate this could have bbeen significant. Certainly there seems to have been a change in the frequency & intensity of glacial cycles around then.

Also at around the time the Drake passage was opening as TIS meantions - changing circulation patterns - a different geological process was occuring - India was crashing into Asia, lifting the Himalayas & the Tibetan Plateau behind them. This is significant for 2 reasons. It probably changed air flow patterns in the region. But also it exposed lots of new rock, allowing the rate of removal of CO2 by chemical weathering on rocks to increase, quite possibly lowering CO2 levels enough to push us into a climate where Ice Age conditions were possible.

And if you want a long term property investment, avoid Denmark, Florida, The Netherlands. But there could be money in and England To Archangelsk ferry service.

My hypothetical time slice of the present represented by a graph showing Temperature and CO2 concentrations could only be moved backwards in time as far as the beginning of the Pleistocene. Any further back and tectonics make it useless. However I believe it would have been futile to examine even this period with an eye to predicting the future behaviour of
our climate by looking for similar conditions in the past.

There are a lot of interesting hypothesis that postulate the consequences of a given set of climatic conditions. But as to cause and effect there are so many, in fact I think there are too many, competing ideas for the average layman to wade through with any confidence in their veracity.

There are only two scenarios that I believe should concern me.
1) A runaway greenhouse effect leading to Venusian conditions.
2) Global cooling
If we are to believe people like Monkton the runaway greenhouse effect is constrained by the past because the climate sensitivity has been limited (who knows by what) or we have to say that there is a lot of uncertainty in the past record and no past conditions match today's conditions to such a degree that it allows us to make such conclusions(low sensitivity).
Back to another Planet.

00

Moderator Response: Please take discussion of your two scenarios to the thread "It’s not bad."

FundME, neither of your two scenarios is even remotely possible under current conditions.

On the other hand, sufficient climate change to cause the deaths of billions of people is theoretically possible. That kind of disruption would also certainly lead to wars which, if nuclear (or worse) weapons were involved, could potentially eliminate our species. If you are not concerned by that then you can indeed ignore climate change.

I should have phrased my last comment a lot better. The two concerns I mentioned were with reference to the past record and not today's world. As I tried to state today's world is so different in might as well be another planet. As we were discussing paleoclimate I just assumed it would be taken for read.
1)Did we have runaway Greenhouse effect leading to Venusian type conditions.
2)Did we have a cooling world leading to Ice ages.
People like Monkton cant assume that because runaway greenhouse effect did not happen in the past it cant happen today as the conditions are completely different.
There that is fixed.

FundMe#16: "today's world is so different in might as well be another planet"

Please clarify this statement, with reference to supporting literature. As it is, it contradicts fundamental principles of sciences like geology, evolutionary biology, cosmology, certain aspects of physics and chemistry, etc.

muoncounter.
Only within this context.
What we can learn from the Last Interglacial time period. Understanding this period may provide clues on how the environment may respond to similar conditions in the future.

Which leads me to believe that you actually agree with people like Monkton that the climate has a low sensitivity response because it has been that way in the past. I just cant see how we can use the past to assert such claims for the future.

If you read my earlier posts and the replys to them you will be able to see how I arrived at this conclusion.

There was an excellent example of the jet stream loop in the north Atlantic at the beginning of October 2011. It could be seen on some weather charts looping up the western side of the Azores high and the eastern side of the Iceland low.
This brought unusually high temperatures to northern Europe and southern UK while Northern Ireland and central Scotland had cloudy, warm frontal conditions.
Now the jet stream has resumed its West-East flow and normal westerlies bring temperatures more usual for this time of year.
One would think a large volume of warm salty water was transported northward during the period.
Thank you for a great explanation of the conditions applicable during these transitions.
Is there a site where real time jet streams can be found. I currently use ugrib weather that shows isobars and rain. Jet stream has to be inferred.

"that the climate has a low sensitivity response because it has been that way in the past."

It has? Cant see that in the published science.

"I just cant see how we can use the past to assert such claims for the future."

Because the laws of physics are same. You use the same climate model for LGM as you use for tomorrow. The initial and boundary conditions are different but the physics and consequent processes are the same.

FundMe#18: "Which leads me to believe that you actually agree with people like Monkton that the climate has a low sensitivity"

You are free to believe what you like, but we try to base our understanding on science. See the science-based thread on paleoclimate and sensitivity. You will note on that thread that paleo data is quite useful in determining a likely range of sensitivity far greater than anything Monckton dreamed up.

muoncounter
Thanks for the read (your link). It increased my doubts about our ability to use the past (paleoclimate) as a predictive tool for the future.

As G Schmidt says.
Simulations of climate over the Last Millennium (850–1850 CE) have been incorporated into the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). The drivers of climate over this period are chiefly orbital, solar, volcanic, changes in land use/land cover and some variation in greenhouse gas levels. While some of these effects can be easily defined, the reconstructions of solar, volcanic and land use-related forcing are more uncertain.

You say, "paleo data is quite useful in determining a likely range of sensitivity"
If we used terms such as "likely range" for the speed of light or to describe the earths gravitational force we would be back in the 17th or 18th century.

Thanks all the same but I think for now I will file my concerns regarding the runaway greenhouse effect or global cooling in the "do nothing but keep monitoring file".

The science of predicting from a known state to a known state has to move on a little before we can predict from a known state to an unknown state.
I will stick with the Past is another planet at least for now.
cheers

00

Response:

[DB] "Thanks all the same but I think for now I will file my concerns regarding the runaway greenhouse effect or global cooling in the "do nothing but keep monitoring file"."

This ranks right up there with:

Continuing to smoke despite the accumulated weight of evidence against it AND all those hot spots on your last MRI...

Continuing to eat those potato chips and bacon you favor despite your most recent cholesterol measurments show LDL levels above 250, Trig's over 1,000 and functional HDL of less than 20%...

Fundme#22: "If we used terms such as "likely range" for the speed of light or to describe the earths gravitational force we would be back in the 17th or 18th century."

So your conclusion is 'we can't know exactly, so we know nothing.' Based on that kind of thinking, the 17th and 18th centuries look like a time of terrific enlightenment. Oh wait, they were.

"I will stick with the Past is another planet at least for now."

Terrific: You came in with a preconceived idea based on factual error, you rejected all science contradicting you and now you are sticking to your original, unsupported (and unsupportable) claim. There are words to describe that thinking process, but I won't list them here. Hint: They are not read, listen, learn, understand.

FundME, if I ask you what Earth's gravitational force will be 10,000 years from now, will you answer with a precise measurement, or will you answer with a likely range?

Your argument can be made about sociology and economics as well, and the same criticisms can be leveled against it. Can studying the European economy of the 19th century tell us anything useful about the European economy of the 21st century? The two periods are quite different. However, there are fundamental elements that are effectively the same in both situations. By recognizing the fundamental elements and carefully analyzing how they played out in their historical and material contexts, we can determine the likely outcome of those elements placed in some future historical and material context (model). A "likely range" is all you're going to get if you or anyone else uses the past in any way to make a prediction for complex phenomena, and that includes your own life from week to week and year to year (and yet, despite the uncertainty, you still plan your life based what has happened in the past, and most of this planning is intuitive rather than scientific, and it all gives at best a "likely range"). You make the determination of when the past is no longer useful for understanding the future. That determination is not an absolute.

And it's not the paleo record that tells us that a "runaway greenhouse" effect is unlikely. See the "Positive feedback means runaway warming" argument thread. I also note that you, FundME, have not yet taken your lack of concern to the "It's not bad" thread.

00

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.